1. Field of the Invention
The present invention relates to a disk drive storage device and more particularly to a circuit for supplying current due to a back electromotive force generated by the spindle motor to the voice coil motor when the power for the disk device is turned off in order to retract the transducer head to the landing area of the disk recording medium or unload it from the disk recording medium.
2. Description of Related Art
A disk drive storage device comprises a disk which is a medium for recording data, a spindle motor for rotating the disk, a head slider, a carriage, a voice coil motor (VCM), a crash stop, etc. within a disk enclosure, and comprises, on the external surface of a disk enclosure, a circuit board (card assembly) on which an MPU, a spindle driver, a VCM driver, a circuit for retracting (hereinafter simply referred to as a retract circuit), etc. are mounted.
The carriage has a head arm for supporting the head slider, and a coil arm for supporting the voice coil of the VCM. The head slider includes a transducer head for performing a data read/write to the disk. The VCM driver drives the VCM by feeding a current (VCM current) through the voice coil. The VCM swings the carriage. The head arm and the coil arm are extending in the direction opposite to each other with respect to the pivot of the carriage. The crash stop is fixed to the disk enclosure, and hit by the coil arm to define the swing range of the carriage.
In the disk drive storage device, the VCM and the carriage move the head slider to above the data area of the disk, and retract the head slider from above the data area and move it to the landing area of the disk. The head slider is floating over the disk surface when the disk is rotating, and it lands on the disk surface when the disk stops its rotation. Disk damage may occur if the head slider lands on the data area of the disk and thus, the head slider must be retracted to a landing area and must land on the landing area when the disk stops its rotation. The VCM current for retracting the head slider is called a retract current.
The spindle driver and the VCM driver operate on the power supplied to the disk drive storage device. The disk stops its rotation when the power to the disk drive is turned off, and the VCM driver also stops its operation, so that the retract current cannot be fed to the voice coil from the VCM driver. When the device power is turned off, the retract circuit feeds the current due to a back electromotive force generated by the spindle motor through the voice coil as the retract current to retract the head slider. The retraction of the head slider by the retract circuit when the device power is turned off is sometimes called power-off retraction to be distinguished from the retraction of the head slider when the power is being supplied. Hereinafter, a simple designation of xe2x80x9cretractionxe2x80x9d means the retraction by the retract circuit when the device power is turned off, and a simple designation of xe2x80x9cretract currentxe2x80x9d means the retract current supplied from the retract circuit.
Even if the device power is turned off to stop the driving of the spindle motor, the disk continues to rotate for a while by the inertia, allowing the spindle motor to generate a back electromotive force. The magnitude of the back electromotive force depends mainly upon the preset rotational speed of the spindle motor. The retract current increases as the current due to the back electromotive force increases, and the swing speed of the carriage increases as the retract current increases. Accordingly, the swing speed of the carriage varies depending on the preset rotational speed of the spindle motor.
When the device power is turned off, the carriage swings the head slider in the direction of the landing area, and stops its swing when the coil arm abuts on a crash stop. When the carriage stops its swing, the head slider is positioned over the landing area, and when the disk stops its rotation, the head slider lands on the landing area.
However, in the above conventional disk device, the swing speed of the carriage in the retraction depends on the retract current, as described above, and the retract current value depends on the preset rotational speed of the spindle motor. Thus, if the preset rotational speed of the spindle motor is large, the swing speed of the carriage in the retraction becomes large, and the shock given when the carriage hits the crash stop becomes large. Conversely, if the preset rotational speed is low, the retract current becomes small, resulting in an unstable retract operation. This has been a problem in increasing the reliability of disk devices when the retract circuit is shared between a plurality of disk devices which are different in the preset rotational speed of the spindle motor.
The above problem can be solved by changing the circuit constants of the retract circuit such as the resistance value according to the preset rotational speed of the spindle motor. However, one problem associated with this approach is that the manufacturing cost of disk drive increases because a different card assembly (a circuit board on which the retract circuit and the like are mounted) must be prepared for each of the disk drives which are different in the preset rotational speed of the spindle motor.
Accordingly, it can be seen that there is a need in the art to provide a retract circuit for a disk drive storage device which can be shared between a plurality of disk drives having different preset spindle motor rotational speeds.
To overcome the shortcomings of the prior art described above, it is an object of the present invention is to provide a retract circuit for a disk drive storage device that can be shared between a plurality of disk drives having different preset spindle motor rotational speeds. It is the further object of the invention to provide a retract circuit that has improved reliability as well as a reduced manufacturing cost.
To accomplish the above objects, the retract circuit of the present invention is characterized in that, if the current due to a back electromotive force which is received from the spindle motor exceeds a predetermined value, this current is clipped or sliced so as to be limited to the predetermined value or below, and the current equal to or below the predetermined value is supplied to the voice coil motor.
One advantage of the present invention is that the same card assembly can be used across disk drives having different rotation speeds for the spindle motor.
Another advantage of the present invention is that it can be implemented without increasing the manufacturing cost of the disk drive storage device.
Still another advantage of the present invention is that it provides a disk drive storage device having a more stable retract operation.
The above, as well as additional objects, features and advantages of the present invention will become apparent in the following detailed written description.